A typical electric cable generally comprises a conductor that is surrounded by one or more layers depending on the application area. E.g. power cable has several layers of polymeric materials including an inner semiconducting layer, followed by an insulating layer, and then an outer semiconducting layer. To these layers, one or more further auxiliary layer(s) may be added. The outer protecting polymeric layer is known i.a. as a jacketing layer. Any of the layers can be crosslinked as well known in the field.
Safety, reliability and long use life are important key factors required for cable applications. As the outer jacketing layer provides the outer protection of the cable, it plays an important role to provide system functionality.
Low density polyethylene (LDPE) which is e.g. produced in a high pressure process has been conventionally used in all types of cable layers including jacketing layers. The drawback thereof is their unsatisfactory mechanical properties required for a protective jacketing layer.
Linear low density polyethylene (LLDPE) is known i.a. as a jacketing layer material. However and typically, also the LLDPE is not fully satisfactory as regards to the mechanical properties required for a polymer in a cable layer, such as a jacketing layer.
The mechanical properties of the layer can be improved by increasing the density of the polyethylene. High density polyethylene (HDPE) polymers indeed provide i.a. improved mechanical strength to a cable layer, such as abrasion resistance. However, HDPE has a disadvantage of limited stress cracking resistance, expressed e.g. as ESCR, and decreased flexibility required i.a. for a jacketing layer.
Multimodal polyethylene (PE) provides one way of tailoring the polymer properties. To enable the use of a multimodal PE in a jacketing layer, the property balance should be optimised i.a. with respect to mechanical properties, such as strength, stress cracking resistance and flexibility, and to processability. Various solutions have been provided, but there is still needs for alternative or improved property balance.
Moreover, e.g. single site catalyst (SSC) offers i.a. controlled incorporation of comonomers which provides a further means for tailoring the polymer. However, the processability of SS catalyst based PE is often problematic.
There is a continuous need in the polymer field to find polymers which are suitable for demanding polymer applications, particularly for W&C applications, where the cable materials must meet high requirements and stringent authority regulations.